A polypropylene resin is a typical molding material having melt processability, mechanical strength, resistance to chemicals, and the like in an excellent balance, but the application to be made of it is limited in the field demanding high temperature resistance.
On the other hand, a polyphenylene ether resin is recognized as an engineering plastic having excellent high temperature resistance and mechanical properties but has a disadvantage of difficulty in molding due to its poor melt-fluidity characteristics.
Hence, a resin composition comprising a polypropylene resin and a polyphenylene ether resin having the respective disadvantages of these resins compensated without impairing the respective advantages would be an excellent molding material of broader application. To this effect, various compositions have been proposed. For example, Japanese Patent Publication No. 7069/67 discloses a composition comprising polyphenylene ether and polyolefin. However, since these two resin components are essentially incompatible with each other, the compounding ratios are limited so that the intended purposes cannot be achieved. Japanese Laid-Open Patent Application No. 88960/79 discloses that a large quantity of a polyolefin resin may be compounded to a polyphenylene ether resin with satisfactory compatibility in the presence of an elastomeric styrene/butadiene/styrene triblock copolymer. However, as described in the publication, if the total amount of the polyolefin and the elastomer exceeds 30% by weight, phase separation is apt to take place and the bending strength is seriously reduced, which is assumed to result in deterioration of stiffness that is an important characteristic of a molding material. Further, Japanese Laid-Open Patent Application No. 103557/83 (corresponding to U.S. Pat. No. 4,383,082) discloses a composition comprising polyphenylene ether, polyolefin, and a styrene/butadiene block copolymer, in which the polyolefin is present in an amount of 20 parts by weight or more per 100 parts by weight of the composition. However, there is still room for further improvement on stiffness, particularly stiffness at elevated temperature, that is subject to the influence of an increase in the ratio of the polyolefin component. Furthermore, U.S. Pat. No. 4,154,712 teaches to combine a low-molecular weight polyphenylene ether resin with a block copolymer of an aromatic vinyl compound and a conjugated diene compound, but the result achieved is confined to improvement on mechanical properties of this two-component system.